A question about Granite

I have a good friend that is a geologist who commented on my granite: "that is definitely NOT granite!"

Anyway, I was chuckling reading some of the posts in the Granite plate thread and it caused me to wonder about a granite plate I have. Granite plates around here are nearly free. The last I actually paid for was a starrett pink AA for $50.

To the point, I was given a 36"x48"x8" plate only because the owner didn't know how to get rid of it. It was used in his mold shop up until last year when he closed it. He wound up putting it outside for about the last year.

This takes me back to my first statement. If it was real granite I wouldn't worry the least about it being outside. Opinions? I dont regularly work closer than .001, if I do I have my pink granite. For an all around shop surface would it be ok having been weathered?

Fal Grunt said:

I have a good friend that is a geologist who commented on my granite: "that is definitely NOT granite!"

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Did he tell you what he thought it was then?

Be like going to the doctor with what you think is a sore throat and he says "That is not a sore throat" and leaves it at that..

As long as it was covered, I wouldn't worry. Like you I was lucky enough to get a large granite plate from a CMM. I would like to get it calibrated before I start using it for inspection. But for 0.001" stuff it's great. If you can still see the shine on it when you look down the plane of the plate it's a good sign.

If not, you may want to get it looked at by a surface plate guy. That is if you can get them to come out. I tried to get the guy from a local surface plate service co. He kept standing me up. No call - nothing. I set up 3 appointments time off work. I was not pleased. I will try again once I get some of my other projects out of the way. Hope this helps to ease your mind. Good luck with yours.

Best Regards,
Bob

I used to sell plates as a distributor for Tru-Stone that is now owned by Starrett and it is granite. I think your friend must have got his degree from Online Diploma for $29.99.

High quality granite: charcoal black, pink, zimbabwe black, academy black, impala black, imperial black, sierra gray

QUARRIES | Rock of Ages Corporation

To a geologist or mineralogist, granite is an igneous rock containing crystalline quartz and feldspar. In contrast, a metrologist considers granite to be pretty-much any igneous rock that can be used to make precision stoneware, whether it contains quartz or not.

In precision-stoneware terms, quartz is relatively hard when compared to the other minerals in common igneous rock, but generally not the stiffest material in the rock. In practical terms, this means that "true granite" -- containing quartz -- is more resistant to wear than hyperesthene gabbro and similar "black granites", but also more flexible.

My recollection -- from a 40-some year ago Geology 1A class -- is that commercial quantities of high-quality "black granites" suitable for making precision stoneware were known to exist in North America in the San Diego, California area, in southern Africa, and in central China, while commercially-viable "true granite" was found pretty much throughout North and South America, Europe, and Asia.

Manufacturers of precision stoneware -- which can often trace their roots to architectural- and tomb- stone businesses -- tended to use rock from nearby quarries as their raw material, and tended to push the advantage of wear resistance if the local quarry produced true granite, or stiffness if the local quarry produced black granite. The Europeans may have been somewhat of an exception, as African black granite was commonly roughed-out at the quarry and shipped to Europe for finishing.

Pyramid Granite of Escondido, California has this to say about types of granite for precision stoneware: General Info and Granite Selection - Pyramid Granite & Metals

Changing the subject only slightly: In my experience, Europeans who speak English as a second language often use the term "marble" or "marble table" to mean "surface plate" or "surface table". Even in Europe, though, I've never encountered a "marble" or "marble table" that was actually made of marble (a very soft sedimentary rock), but were always made of either true or black granite.

John

Crossing the granite thread with another, I might wonder if the surface plate is more stable if it's been sitting out behind the factory for several years. And I suppose I could argue for stability since it's been sitting outdoors aging for several million years. OTOH, I'm no authority, having failed my geology class - I guess I took too much for granite.

John,

That is an interesting link you posted to Pyramid particularly with respect to Black Granite and its greater stiffness and finer grain and reduced porosity and the indication that many of the lighter colored granites are cheaper and more porous but also more wear resistant. I had assumed that since the Chinese stones I own were made of black granite, that it was chosen because it was cheaper and I also assumed it might be less preferable than the pink or other colors. If Pyramid's assessment is true, the black is better except for wear resistance. Comments?

I recently picked up a granite surface plate for free to deliver to a friend. The donor was a retired machinist who has no flat scraping experience but a wide variety of general machining experience and lapping experience. He admonished me to be sure not to get the granite wet as the weather was threatening and the stone was in the open bed of my truck. This concern struck me as odd in that I would have assumed the granite was relatively immune to water. Can any one comment on that concern? Valid?, not a real concern etc.... I could see the granite maybe absorbing a small amount of water and maybe taking a few days to evaporate. Is there more to this? It stayed dry, BTW.

Denis

A granite surface plate for the most part is impervious to weather in so much as weather will not cause lasting change to the plate ( I'm not referring to long term storage out in the elements ) it will how ever cause some disconcerting problems. Though it really doesn't "absorb" moisture, it will take some time for any to evaporate out of the plate and could add to rust problems on items placed on the surface plate until it does so. Heat on a surface plate can cause a much more troubling condition, a temperature gradient from top to bottom or from the center to the out side of the plate can cause an alteration in the flatness of the surface that remains unnoticed and remains until the plate reaches thermal equilibrium.
Cheers Don

Yeah, what Don said.

Leave a height gage overnght on a faintly damp granite plate and you'll have a rust print permanently tattooed on the reference surface by morning. That rust print follows porousity into the surface. It may linger for two calibration cycles and everyone that happens by will point at it and smirk. It's like walking around with a yard of imperishable toilet paper stuck to your shoe for two years

Planolith (German manufacturer) doesn't call it granite. They call it "hard stone".
Natural granite

Edit:
Funny, now the link shows as "natural granite". In German, it still is "natural hard stone". Maybe there is a difference between granite here and over the pond.


I still call it granite, despite knowing that a geologist might not call it that way. Only if I'm really picky (that happens almost never) I call it hard stone.


Nick

The State of Texas has a capital building made of pink granite. Been standing for over 100 years! To date, I have not heard of any issues of cracked or damaged granite due to water or any other acts of nature.

Just west of Austin, in Marble Falls or Granite Shores they call it, resides the largest pink granite quarry in the world.
I have a chunk of it with the name "Starrett" on the label. (wife finds out, it will be my grave marker when she get finished with me)

We have a lot of red granite in our area. Some older buildings made of it. If the granite absorbed any moisture, it would crack quickly. Sandstone will pop in the winter sometimes, I would not worry about granite.
Joe

A rose by any other name....

"Granite" in this instance is a generic term, like "Kleenex," "Bullard," "Bridgeport," or "Blanchard;" nouns not srictly accurate but generally accepted to refer to a broader category. The requirements needed for our purposes are a hard, stiff, stable, strong near imperveous, chemical resistant, varigated, granular igneous rock avalable in deposits economical to quarry that are suitable for metrology products. There may be a wide range of suitable quarry stones that only an obsessive/compulsive geologist would differentiate and rant about but for dullards like us "granite" is close enough.

In any case, a cheap import granite surface plate costs 1/10 the price of an equivalent new domestic cast iron scraped surface plate and has 5x the wear life in general shop service at the penalty of double or more the unit weight. No brainer; intrusive igneous felsic, phanteric granite or intrusive black gabbro having suitable proportions of amphibole, pyroxene, biotite mica, plagioclase and olivine - who cares?

Denis --

Pyramid Granite's assessment of the relative technical merits of black granite v true quartz-bearing granite is consistent with the precision-stoneware industry's conventional wisdom, although we should remember that their corporate point of view may be shaded ever so slightly by their proximity to North America's black-granite quarries.

I don't think I should even hazard a guess as to the economics of black granite v true granite for precision stoneware. I do believe that the world's supply of black granite suitable for precision stoneware is smaller than the world's supply of true granite suitable for precision stoneware, which might suggest that a specific volume of black granite still in the ground might sell for a higher price than the same volume of true granite still in the ground . . . but it may well cost more to extract that volume of true quartz from the ground because the harder true quartz might be more time-and-tool-consuming to cut. I think it reasonable to presume that the final finishing of the quarried blocks would have analogous cost differentials.

(As an aside, some number of years ago I spent a couple of weeks in and around Xichang, China, and while there saw a fair number of large trucks loaded with cocoa-brown boulders on the highway. The boulders, which were in the neighborhood of 2 to 2 1/2 meters across, were en route to one of many small saw-and-polish facilities that diamond-cut them into plates, using a 3-meter-or-so circular saw -- dry, and talk about a dust cloud -- that remained attached to an uncut section of the boulder. The partially-cut boulders were then dragged a few meters to an open-sided metal building, where the plates were broken off and carried to a vertical-spindle wet grinder on a "broken arm". The sawing-and-grinding facility I visited covered, at most, an acre and a half, and nobody there spoke English. They were quite happy to let me wander around, but didn't want me to take any pictures. Their product was "architectural stone veneer", and despite being sawed out of cocoa-brown boulders, polished up into a beautiful, fine-grain black that struck me as darn-near ideal material for precision stoneware.)

As for weather resistance, igneous rocks are commonly used for breakwaters, and as long as they're not cracked a few annual freeze-thaw cycles shouldn't hurt them at all.


Forrest --

Olivine? Olives grow on trees.


John

John Garner said:

Forrest --

Olivine? Olives grow on trees.

John

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Yabbut they've got stones in the middle of them...


and now back to our regularly scheduled programming.

John Garner said:

Forrest --

Olivine? Olives grow on trees.

John

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Not responsible. Everything I seem to know is actually pasted from Google,

Richard, with all due respect I have a good deal of background in geology, enough to know whether he has a clue or not. Neither the Smithsonian or USGS thought his degree(S) were of the $29.99 variety. While my background is NOWHERE as extensive as his, I have a great deal of respect for him, and he is extremely knowledgeable.

Probably somewhat similar to someone telling you that you must have leaned scraping at a $49.99 seminar.

If he tells me it isn't granite by composition I believe him. The next time someone drops a plate at work and chunks a corner I'll send it out to him for analysis.

Thanks everyone else for the lively discussion. I think based on everyone's response it's worth saving and moving. I should be moving it from a friends shop to another location. Once I get it set up I'll check it over.

I am curious to see if I can get a inspector to come out to my shop. I'd love to know how my old "master" cast iron surface plate is holding up.

Well Fall with due respect,

You wrote:

I have a good friend that is a geologist who commented on my granite: "that is definitely NOT granite!"

Then you wrote;

"This takes me back to my first statement. If it was real granite I wouldn't worry the least about it being outside. Opinions? "

I gave you my Opinion and trying to stay with-in the forum rules, that was the only way I could say what I was thinking politely.

Anyone who is in the machine tool business and hears,

"that is definitely NOT granite!"

From my experience and who has toured a Granite plate manufacture like Tru-Stone and knows it is stone GRANITE then I assumed the guy was clueless. That was my opinion on his remark. Why don't you send him a link to this thread so he can get an education on Granite Stone used in the Machine Tool Industry and ask him to join explain what he meant. Maybe he has never seen polished granite and only in the raw state? I am not trying to start a argument but you asked and I answered. Rich


PS:

To All I found this info now and got a charge of the story on the right side. The history of granite plates:
Quality Digest Magazine

Denis
I'm glad you got it home OK, for the rest of you, it was off the CMM I just picked up from Boeing 43" by 12" by 8" I part I wanted was the big flat and table it's 39 by 30 by 8 and sitting on 3 points.

John

Richard King said:

<>

To All I found this info now and got a charge of the story on the right side. The history of granite plates:
Quality Digest Magazine

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Would you care to elaborate as to what is "on the right side" compared to prior linked pages? All the linked pages have quite a bit of information on them and it is unclear to me what you mean to point out. It must be of some importance to you or you would not have taken time to post the link and make the comment.

Denis